A wireless communication system has been developed into a high speed and high quality wireless packet data communication system to provide a data service and a multimedia service as well as a basic voice service. Recently, various wireless communication standards, such as high speed downlink packet access (HSDPA), high speed uplink packet access (HSUPA), long term evolution (LTE), or long term evolution advanced (LTE-A) in 3GPP, high rate packet data (HRPD) in 3GPP2, or IEEE 802.16, have been developed to support the high speed and high quality wireless packet data transmission service.
The LTE system, which has been developed to effectively support the high speed wireless packet data transmission, may maximize the capacity of the wireless system by utilizing various wireless access technologies. In addition, the LTE-A system, which is the advanced wireless system of the LTE system, has an improved data transmission ability compared to the LTE system.
The existing third wireless packet data communication systems, such as the HSDPA, the HSUPA, and the HRPD, use an adaptive modulation and coding (AMC) method and a channel sensitive scheduling method in order to enhance the transmission efficiency. At this time, according to the AMC method and the channel sensitive scheduling method, a proper modulation and coding scheme may be applied at a time determined to be most effective by receiving the feedback of partial channel quality information from a receiver.
A transmitter, in the wireless packet data communication system to which the AMC method is applied, may adjust the amount of transmission data according to the channel state. That is, in a bad channel state, the transmitter may reduce the amount of transmission data to thereby maintain the reception error probability within desired level. In addition, in a good channel state, the transmitter may increase the amount of transmission data to effectively transmit a lot of information while maintaining the reception error probability within a desired level.
In the wireless packet data communication system to which the channel sensitive scheduling resource management method is applied, since the transmitter may selectively provide a service to a user in a good channel state among a plurality of users, the system capacity can be increased compared with a method in which the channel is allocated to a single user for a service. Such an increase in the capacity is called a multi-user diversity gain. The AMC method may include a function of determining the number of spatial layers or the ranks of a transmitted signal when it is used together with the multiple input multiple output (MIMO) transmission method. In this case, the wireless packet data communication system applied with the AMC method may determine an optimal data transmission rate by considering the number of transmission layers using the MIMO as well as a coding rate and a modulation scheme.
In general, the OFDMA method can expect an increase in the capacity, compared to the CDMA method. One reason that the increase in the capacity is expected in the OFDMA method is that frequency-domain scheduling can be performed. The capacity gain is obtained through the channel sensitive scheduling method according to the characteristic in which the channel varies with time. Likewise, the more capacity gain may be obtained by utilizing the characteristic in which the channel varies with frequency. Accordingly, vibrant studies for converting the code division multiple access (CDMA), which is a multiple access method that has been used in the second and the third wireless communication systems, into the orthogonal frequency division multiple access (OFDMA) in the next system are in progress. In addition, the 3GPP and the 3GPP2 began to proceed with the standardization of the evolution system for using the OFDMA
Meanwhile, the LTE-A system has provided CoMP transmission technology in which a plurality of cells performs cooperative transmission with respect to a terminal addition, in the case of the CoMP transmission technology, the terminal may be allocated with a plurality of CSI-RSs in a resource block transmitted from a base station to the terminal for the effective channel estimation from a plurality of cells, and thus, a COMP data transmitting and receiving method considering a plurality of CSI-RSs is required.
In order to effectively use the CoMP scheme in the LTE-A system, it is required to receive the downlink data, for example, a physical downlink shared channel (PDSCH), in consideration of channel state information reference signal (CSI-RS) resources transmitted from the cells corresponding to a plurality of transmission points.
However, in the current LTE-A system, since the PDSCH signals are received on the assumption that the downlink data is not mapped in all of the CSI-RS resources allocated to the terminal, the allocation of a plurality of CSI-RSs may cause a waste of resources.